This invention relates generally to marine cylindrical shaft liquid seals, and more particularly to a gear shift shaft liquid seal in a stern drive bell housing.
One of the major marine stern drive propulsion systems manufacturers distributing under the trademark Mercruiser has had an ongoing problem with a particular liquid seal around the gear shift shaft disposed within the bell housing of stern drive units. This bell housing is generally pivotally connected to the transom mounting plate of the stern drive unit and houses two parallel adjacent passageways. The upper passageway is provided to accommodate the drive train gimbal or universal, while the lower passageway is adapted to convey exhaust gasses and heated sea water from the engine. The gimbal passageway is designed to be watertight or water free, while the exhaust passageway is designed to have sea water passing therethrough.
A gear shift shaft is mounted vertically within the bell housing having its upper portion supportively mounted within a partition between and partially defining the gimbal and exhaust passageways and having its lower portion supportively mounted in an aperture at the bottom of the exhaust passageway. As a result, the main central portion of the gear shift shaft is exposed to both exhaust gasses and heated sea water.
Disposed at the upper end of the gear shift shaft is an elongated shift lever which laterally extends and is connectable at its distal end to a gear shift cable which itself extends to the throttle and gear shift levers at the helm of the boat. To prevent sea water entering the gimbal passageway past the gear shift shaft at the partition, the manufacturer now provides a cylindrical brass bushing for forceable insertion into the aperture in the dividing partition between gimbal and exhaust passageways. The cylindrical bushing includes a central hole therethrough for snug fitting around the gear shift shaft. This brass bushing is slightly thinner than the thickness of the dividing partition so as to accommodate a single rubber o-ring or oil seal below the bushing. One version of this oil seal incorporates an inner metal cup encapsulated by rubber on all surfaces to provide a liquid seal both against the gear shift shaft and the dividing partition aperture.
Although this conventional bushing/seal arrangement in its early stages of use is reasonably effective, eventually electrolysis and deterioration occurs between the seal and aperture in the partition and the seal fails. In such circumstances, the replacement with another identical seal is effective for only a short period of time, if at all. The deteriorated partition aperture is unable to effectively retain a new seal in place and resort is frequently made to bonding agents such as epoxies and the like to assist in retaining the replacement seal in place. However, this is only a one-time fix whereupon at the next seal failure, the entire bell housing must be replaced.
The net effect of deterioration of these conventional seals is that sea water enters into the gimbal passageway and into the shift cable connected to the shift lever. Thereafter, rapid deterioration between the casing and the core of the shift cable occurs resulting in binding and ultimate failure of the shift cable which must also then be replaced.
The present invention provides an improved liquid seal for this environment which is adaptable to both service and supplant both the brass bushing and the conventional seal and may also be incorporated into O.E.M. components at manufacture.